I'm sorry to hear you've been through this too.
I've always had one breast bigger than the other and this is the armpit where I've noticed the "swelling" - when I put my arms down there's much more of a definite bulge on the right side. I also notice it when I put my arms up in the air and turn my head but nobody else seems to be able to see it?! I'm on the pill and the breast pain normally kicks in 2 weeks before my period but the pain is still present now I've started a new pack after my weeks break.
I've also noticed the pain is radiating around my shoulder, upper back and arm...
I'm just finding it so hard to believe that nothing's there... Even though 3 people (one being my GP) have checked my armpits and breasts for lumps.